The royals as babies: the Queen Mother with Queen, the Queen with Charles, Charles with William, Carole Middleton with Kate, Lady Di with Harry. Pictures: Getty Archive Source: Getty Images

THE timing of the royal pregnancy has caused a bizarre legal twist that may leave the future of the baby in the hands of New Zealand.

The tiny Commonwealth country, half a world away from Buckingham Palace, is co-ordinating unfinished succession law changes in 16 realms.

If Prince William and the Duchess of Cambridge have a daughter and then a son as a second child, the little princess would only become Queen if New Zealand can successfully co-ordinate the changes and end a three centuries-old succession law that says royal daughters be passed over by younger male siblings.

Should Wellington fail to work quickly enough, constitutional monarchist David Flint believes the result could be messy, as it was in Sweden where succession laws were changed in 1980, demoting a baby prince behind his older sister, Crown Princess Victoria.

Prime Minister Julia Gillard's spokeswoman said Australia would have the law change before parliament next year.

Ms Gillard will finalise legislation with state premiers at a Council of Australian Governments meeting later this week.

The change, of which the Queen approves and which is driven by UK Prime Minister David Cameron, was agreed to at a Commonwealth Heads of Government meeting in Perth last year.

A spokeswoman for NZ Prime Minister John Key said the country's cabinet secretary was "charged with implementing" consistent succession laws in the realms, with New Zealand legislation expected to go before parliament early next year.

Law changes are advanced in most Commonwealth countries including Australia, New Zealand, Canada, Jamaica, Antigua and Bermuda, the Bahamas, Grenada, Belize, St Christopher and Nevis, St Lucia, the Solomon Islands, Tuvalu, St Vincent and the Grenadines and Papua New Guinea.

Presuming the laws are successfully changed in all countries, they can be backdated.

But while Prince William may have had the expectations of the Commonwealth on his shoulders, uppermost in his mind would have been his pregnant wife.

Instead of keeping the pregnancy a secret to tell the royal family on Christmas Day, the news was released after a day of drama when William had to rush Kate from her parents' Berkshire home to London's private King Edward VII Hospital as she fought severe morning sickness.

After consulting his private doctor, the worried prince - tailed by his security team - drove his wife to hospital, where she was reportedly placed on a drip to replace lost fluids after suffering intense vomiting over the weekend.

St James's Palace, which would not say when the baby was due, confirmed the Duchess was being treated for hyperemesis gravidarum, which causes dangerous levels of dehydration in pregnant women.

The Duchess, 30, last night remained in hospital, where she was understood to be under the care of obstetrician Marcus Setchell, surgeon to the Queen for 18 years.

While the pregnancy has sealed what has been a magnificent year for the British monarchy, its announcement broke with strict royal protocol.

Etiquette dictates the Queen should be the first to know but because Kate was ill and her condition deteriorated while staying with her parents, it was unintentionally the in-laws, Michael and Carole Middleton, who were the first to find out.

Sources said William and Kate had planned to announce the good news when the royal family was at Sandringham at Christmas. By then, she would have had her all-important 12-week scan.

Members of the royal family - including the Queen and grandfather-to-be Prince Charles - were informed less than an hour before the statement was put out about 4pm London time on Monday.

Uncle-to-be Prince Harry, serving in Afghanistan, was told by email.

Outside the hospital, police had to hastily erect barriers to hold back more than two dozen live cameras from a variety of the world's media that rushed to the central London hospital after the announcement, but also dozens of local well-wishers.

The Duchess had a number of engagements this week, including a visit to London's Docklands tomorrow for a charity fundraising session on a brokers trading floor, but they have all been cancelled.

The baby news led to national jubilation in the UK with messages of support coming in from around the world from US President Barrack Obama and his wife Michelle and other world leaders through to ordinary Britons via websites and Twitter feeds.

"I'm delighted by the news that the Duke and Duchess of Cambridge are expecting a Baby, they will make wonderful parents," British Prime Minister David Cameron tweeted shortly after the announcement was made by St James Palace.

He later said he had been advised by a paper slipped to him during a meeting and he added: "I'm sure people round the country will be celebrating with them tonight."

And many did, flooding websites with messages of congratulations.

Rumours of a pregnancy had been rife for days since the couple's tour of South East Asia where Kate twice turned away a glasses of wines for a formal toast and instead raised a glass of water.

Bookies suspended betting on whether there would be a royal birth in the new year on the grounds that couple looked "broody".

Last night, betting agencies in Britain were already running books on the likely baby name and colour of hair.

Favourite names are Frances and John, both at 9/1, while Charles, Victoria and George are 10/1. Elizabeth is also expected to be a strong place while royal watchers expect Diana to be a second name if it's a girl.

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